Quantifying strain on posterior shoulder tissues during 5 simulated clinical tests: a cadaver study

Area of Science:

• Biomechanics of the shoulder joint.
• Musculoskeletal anatomy and function.

Background:

• Clinical tests are used to assess posterior glenohumeral joint (GHJ) tissue tightness.
• The direct assessment of posterior capsule flexibility using these tests is not well-established.

Purpose of the Study:

• To quantify strain on cadaver posterior shoulder tissues during simulated clinical tests.
• To compare strain across different posterior GHJ capsule conditions: native and experimentally contracted.

Main Methods:

• Controlled laboratory study with repeated measures on 8 cadaver shoulders.
• Strain gauges instrumented the posterior shoulder tissues (muscles and capsule).
• Five simulated clinical tests were performed under three conditions (native capsule, contracted capsule, and posterior muscles).

Main Results:

• A significant interaction between tests and conditions was found in the middle posterior shoulder region.
• Strain was greater in the contracted capsule condition with internal rotation and humerus flexion compared to internal rotation and humerus abduction.
• Internal rotation in abduction and the GHJ resting position showed greater strain in the lower posterior shoulder region than cross-body adduction.

Conclusions:

• Strain on the experimentally contracted posterior GHJ capsule is maximized during combined internal rotation and humerus flexion.
• Findings provide biomechanical insights into posterior shoulder tissue response during clinical assessments.